1. Field of the Invention
xcex2-carrageenan, which is understood to be the idealized, nonsulfated member of the carrageenan family and the D,D-stereoisomer of agarose, consists of multiple units of carrabiose. Carrabiose contains 1,3-linked xcex2-D-galactopyranose and 1,4-linked 3,6 anhydro xcex1-D-galactopyranose units. xcex2-carrageenan has been reported to occur in segments of natural carrageenans from marine macroalgae, but has never been isolated in pure or even in purified form where the sulfate ester content is less than 2% by weight.
2. Statement of Related Art
In an article by Greer et al., xe2x80x9cCharacterization of Hybrid (Beta-Kappa-Gamma) Carrageenan from Eucheuma gelatinae J. Agardh (Rhodophyta, Solieriaceae) Using Carrageenases, Infrared and 13C-Nuclear Magnetic Resonance Spectroscopyxe2x80x9d, Botanica Marina, XXVII:473-478 (1984), components of carrageenan from Eucheuma gelatinae were identified, including the presence of xcex2-carrageenan and xcex3-carrageenan (a 6-sulfate precursor of xcex2-carrageenan) using analytical techniques such as infrared and 13C-nuclear magnetic resonance, and the use of carrageenases.
Mollion et al., xe2x80x9c13C NMR study of the heterogeneity of the carrageenan from Rissoella verruculosa (Bert.) J. Ag. (Rhodophtya)xe2x80x9d, Food Hydrocolloids, 1:413-421 (1987) conducted a 13C-NMR study of carrageenan obtained from Rissoella verruculosa and obtained several fractions using fractionation techniques. All fractions contained relatively high levels of sulfate, and Mollion, et al. make it clear that they could not separate xcex2- from xcfx89-carrageenan by DEAE Sephadex(copyright) fractionation. See page 420, second paragraph under Table III.
Shi et al., xe2x80x9c13C-NMR Spectroscopic Analysis of Carrageenans from Chinese Eucheuma Speciesxe2x80x9d, Oceanologia et Limnoligia Sinica, 18, 3:265-272 (1987), in English translation, determined the compositions and structures of carrageenans without purification (including xcex2-hybrids) from several species of Eucheuma using 13C-NMR spectroscopic analysis.
Zablackis et al., xe2x80x9cThe Carrageenan of Catenella nipae Zanard., a Marine Red Algaxe2x80x9d, Botanica Marina, XXIX:319-322 (1986), identified carrageenan from the red alga Catenella nipae Zanard as xcex1-carrageenan in which the 1,4-linked units consist entirely of 3,6- anhydrogalactose 2-sulfate and the 1,3-linked galactose units are not sulfated, and illustrates structures of the xe2x80x9cxcex2- familyxe2x80x9d.
Processes have now been discovered for the preparation of both purified xcex2-carrageenan, i.e. xcex2-carrageenan containing from 1% to less than 2% by weight of sulfate ester, and substantially pure xcex2-carrageenan, i.e. xcex2-carrageenan containing less than 1% by weight of sulfate ester.
Purified xcex2-carrageenan can be prepared by reacting a marine macroalga that contains xcex2-carrageenan and/or a precursor thereof with an alkaline compound to convert a precursor present to xcex2-carrageenan, extracting carrageenan from the macroalga, treating the extracted carrageenan with an aqueous quaternary ammonium salt to form a precipitate and an aqueous solution, separating the solution from the precipitate, and isolating purified xcex2-carrageenan from the solution.
The substantially pure xcex2-carrageenan is obtained from the above purified carrageenan by treating an aqueous solution of purified carrageenan with an insoluble ion exchange agent that selectively removes the more highly sulfate ester-containing carrageenans from the solution, and extracting substantially pure xcex2-carrageenan from the solution remaining after separation of the ion exchange agent.
This invention also comprises purified and substantially pure xcex2-carrageenan per se.